Fly Fishing the Henry's Fork



by Mike Lawson


By the first week of June the salmon fly hatch should be in the canyon section above Mesa Falls and starting to show in the Box Canyon. The rainbows of the canyon are some of the fastest growing anywhere and with catch and release, the prospect of catching a lunker is good. This is demanding fishing and you have to really cover the water. The big rainbows can be holding anywhere. Black Rubberlegs, Kaufman's Stone Nymph and Peacock Simulators in sizes 2,4 and 6 are my favorite weighted nymphs for this time of the year. For streamers use Woolhead Sculpins, Woolly Buggers and Zonkers with a sink tip line.
Golden Stoneflies start showing up in mid June. This hatch isn't concentrated in the Box Canyon and the peak of activity doesn't start until mid July. These flies are smaller and patterns in size 6-10 work best. You won't see many golden stones on the water because the hatch extends over about two months, the fish get pretty accustomed to looking for them. Some of the best action on golden stone dries is the last two weeks of July.

After the golden stonefly hatch is over your chances of catching a big trout on a dry fly in the Box Canyon are diminished. The canyon is so rich in aquatic life that the larger fish won't waste time holding near the surface looking for smaller insects. Sculpins, minnows, stonefly nymphs, caddis larva, leeches, crayfish, mayfly nymphs and other aquatic creatures are abundant.

From early August through October your best chance of catching a lunker rainbow will be with nymph and streamer patterns. Use smaller stonefly nymph patterns later in the
season after the adults have hatched. Best nymph patterns include Black Rubberlegs, Kaufman's Stone Nymph, Golden Stone Nymph, Prince Nymph, Zug Bug, Peekimg Caddis and Hare's Ear. Favorite streamers include Woolly Buggers, Flasha-buggers, Woolhead Sculpins, Zonkers, Bunny flies, Muddlers and Marabou Leeches.

The fishing is good throughout the entire season in the Box Canyon. The rainbows are strong and in excellent condition. Early in the season in June and late season in September and October offer the best chance at a real large trout.


From the Riverside Campground, which is about 4 miles below the Harriman State Park, downstream to the confluence of Warm River, the Henry's Fork drops about 1000 feet in elevation. This includes about 15 miles of water. Most of this area is inaccessible and requires some hiking into a steep canyon. The water is very similar to the Box Canyon and the same flies and fishing techniques apply. The best time to fish this section is early in the season when the salmon flies are out and again in autumn.

Below Warm River the river takes on a different look with more defined pools, runs and riffles. The salmon fly hatch is a major event here and occurs when the season opens in late May. This is a good area to float, but if you can't float the access is very good and most of the water is wadable. This section of river has a large population of trout, but since it isn't under the protection of special regulations, the size is small. There are some real lunkers, however, with browns, rainbows and a few cutthroat trout. This part of the river is not greatly influenced by insect hatches. You will find the smaller trout eager to take attractor dry flies throughout the season and your best success at big fish will be with nymphs or streamers. Use the same patterns as described for the Box.


The character of the river changes again from the town of Ashton down to St. Anthony. The power dam at Ashton turns the water below into a tail water. The water temperature is constant providing a fertile environment for abundant aquatic life. I believe this part of the river is richer than any place else, including Box Canyon. Even though it doesn't enjoy the protection of special regulations, there are still plenty of large trout.

Much of this water has the look of a large spring creek with long flats and numerous weed beds. Many of the same hatches occur here as are found in the upper river including salmon flies, tremendous caddis hatches, Green Drakes, Pale Morning Duns, Flavs and Blue Winged Olives. In addition you'll find an excellent Grey Drake spinner fall during the evening hours in late June. The only drawback of this part of the Henry's Fork is during the mid summer when irrigation demand is at its peak, there is too much flow for the fish to hold at the surface and too many weeds to fish underneath. The fishing will be good through early July and then again from mid September on.


The flat meadow water of the Harriman State Park, or Railroad Ranch as it was previously known, encompasses some of the finest dry fly fishing in the world. This kind of fishing is not for everyone, however, as these rainbows can be very selective and unpredictable. They've destroyed the egos of some of the world's finest anglers on more than one occasion. This meadow water extends for about 9 miles, starting at Last Chance below the mouth of Box Canyon and extending downstream to the summer home area of Pinehaven. The season on the Harriman State Park property always opens on June 15 but the flat water surrounding the park opens the same as general season.

The first hatches to occur on this flat water are caddis and three kinds of mayflies. We always see caddis on the water even before general season opens. There are also plenty of small Blue Wing Olive mayflies. Another larger mayfly of the Rithrogena family, commonly called the Black Quill, hatches in early June. This hatch is usually over by the time the ranch water opens. The Pale Morning Duns normally start the first week of June. If you plan to fish this area prior to June 15, the water above the ranch at Last Chance and from the lower boundary down to Pinehaven provides some excellent early dry fly fishing. Best patterns for this time period include size 14-16 Hemingway Caddis and Peacock Caddis. You'll also need some mayfly patterns which include size 18-20 Blue Wing Olive No-Hackle and Thorax, size 12-14 Quill Gordon, and Pale Morning Duns in size 14-16.

The most famous hatch, the Green Drake, generally has started when the ranch opens. The hatch usually lasts for 10 days to two weeks. Like other large insects it usually takes the big fish a few days to get accustomed to feeding on the big mayflies. The hatch starts about 11 am and will last only an hour or so unless the weather is cool and cloudy, which will extend the hatch. If you happen to be here when the weather is overcast, count your blessings as you are one of the privileged few. For the Green Drake hatch you'll need some nymphs, emergers, duns and spinners. Most anglers opt for size 10 but I generally lean toward smaller size 12 patterns. My favorite flies are the Green Drake Emerger, Green Drake Cripple and standard Green Drake.

Several other hatches occur during this same time period. The Pale Morning Duns, Blue Wing Olives and caddis usually continue throughout the month. In addition to the previously mentioned caddis hatches, you can expect to find good numbers of tiny micro caddis hatching near the stream banks in the early evening. I've found a size 18 or 20 Spent Partridge Caddis to be the ticket when these little flies are out. The big Brown Drakes also hatch in the evenings during this period. Look for them in the slow sections of the river. Best areas include the islands, bonefish flats, the ranch buildings, the gravel pit and woodroad #16. You'll need nymphs, emergers, duns and spinners for the Brown Drakes. The hatch occurs at the same time as the spinner fall so you may find one fish eating emergers and another keying on spinners. My favorite pattern is Mike's Brown Drake in size 10.

One of the best mayfly hatches of the entire season comes right on the heels of the Green Drake. It's a slate wing olive mayfly, Ephemerella flavilinea, commonly called a "Flav", that looks like its larger cousin the Green Drake. You'll find the Flavs hatching in the late afternoon hours on the ranch. This hatch will continue throughout July. The Pale Morning Dun hatch tapers down in early July and then picks up again later in the month.

August brings some important changes in the fishing on the ranch. By August many of the large trout which hold in the upper section of the ranch near Last Chance start to move downstream. I don't know the reason for this but I'm convinced it happens. If you walk into the ranch from the upper parking lot, you may not find much going on but if you walk into the flats from the mail box, you should find plenty of trout rising in the morning hours. There are two important mayflies to consider during this period, Callibaetis and Tricos. The spinner fall is of the greatest importance with both of these mayfly species. The Tricos get on the water about 8 am. Use size 20 and 22 Trico Spinners. You'll find the Callibaetis spinners on the water about 10 am. Use a size 14 or 16 Callibaetis Spinner or an Adams. Terrestrial will really gain importance in August. You'll frequently find ants, hoppers and beetles on the water.

The Callibaetis and Tricos will continue into mid September, which then brings in hatches of Blue Wing Olives and Mahogany Duns. The Mahogany Dun hatch is of major importance. No-hackles and thorax patterns in size 16-18 work great as well as the standard Red Quill. These hatches will continue until the fishing on Harriman State Park closes on October 15.

There are other considerations when fishing the Harriman State Park in addition to understanding the hatches. You need to be able to locate specific trout and stalk them. Just covering the water is usually unproductive. They can be difficult to catch but the excitement is in the challenge.
In addition to matching the many hatches, you should be prepared with a general assortment of patterns. My favorites include Royal Wulff #16-20, Adams and Parachute Adams #14-18, Renegade #16-20, Black Beetle #14-18, Olive Humpy #16-20, Pheasant Tail Nymph #14-18 and Woolly Bugger #6-10.


The smaller streams in the Henry's Fork area are another sleeper. Warm River and Falls River are two of my favorites but there are several others. These streams offer great dry fly and nymph fishing throughout the summer and you'll seldom see another angler. Some areas have restricted access so you might have to do a little hiking to get to some of the best spots, but it's well worth the effort.

Warm River is a small spring-fed stream that flows out of a small canyon and enters the Henry's Fork above Ashton. There is a nice campground near the confluence. It gets heavy fishing pressure near the campground so you'll need to walk up from the campground or down into the canyon above. Warm River is pocket water with a good population of pan sized trout. You have the possibility of catching 4 species: rainbows, browns, brookies, and cutthroat, all in the same day. Wulffs, humpies trudes and hoppers are my favorite dry flies. Hare's Ear nymphs and Prince Nymphs work well for subsurface action. Since Warm River is spring-fed, the best fishing starts early and continues throughout the season.
If you're a lunker hunter you probably won't waste your time here because the trout will average 8 - 12 inches. I really enjoy spending time on these smaller streams with an ultralight rod, however.


If you like to tube, there are several great lakes in the area. Island Park Reservoir is close by and offers great fishing. The flyfishing is best in the weed beds on the end where the water is shallow. There are usually Callibaetis on the water from late June on in the morning hours. A size 16 Adams is the only dry fly you need if the fish are gulping on the surface. If the fish aren't rising you'll need a fast sinking line withsome leeches and woolly buggers. The fish are mostly rainbows and will average over two pounds. Six pound fish are not uncommon and will feed on the surface when the Callibaetis are out.
Henry's Lake is a great lake to fish for cutthroats and hybrids which average about two pounds and can get larger than ten pounds. The fishing is usually spotty early in the season but really starts to pick up when the damsel fly nymphs get active in late June. You need a medium sinking line to fish the damselfly nymphs, leeches, woolly buggers, shrimp and woolly worms. In September the brook trout start to concentrate near the spawning areas. Best fishing for them is early in the morning just at day break and again before dark.